It is the aim of this investigation to characterize nucleotide sequences in ribosomal RNA (rRNA) both in terms of spatial and functional relationships. Our experiments using molecular hybridization and comparative fingerpring analysis have shown that the rRNA sequences involved in heterologous hybridization share certain features of nucleotide sequence in common in all eukaryotic species studied so far. We wish to localize theseconserved rRNA regions and coorelate them with functional roles of rRNA; this will be done by electron microscopic mapping and also nucleic acid sequencing. We also are studying conservation of secondary structure by gel electrophoresis coupled with the above methods. BIBLIOGRAPHIC REFERENCES: Mowbray, S. L., Gerbi, S.A., and Landy, A. Interdigitated repeated sequences in bovine satellite DNA. Nature 253: 367-370 (l975). Gerbi, S. A. and Crouse, H.V. Deletion of ribosomal RNA cistrons in Sciara coprophila (Diptera). Abstract in press in J. Histochem. Cytochem. (1975).